A swash plate variable-capacity compressor used in an air conditioning system of an automobile or the like is provided with a rotating shaft driven by the rotational power of an engine, a swash plate connected so that the inclination angle thereof with respect to the rotating shaft is variable, a compression piston connected to the swash plate, and other components, and by varying the stroke of the piston by varying the inclination angle of the swash plate, the discharge amount of refrigerant gas is controlled.
The inclination angle of the swash plate can be continuously varied by appropriately controlling the pressure in a control chamber through use of a capacity control valve opened and closed by electromagnetic force to adjust the balance of pressure acting on both sides of the piston, while utilizing the suction pressure of a suction chamber for drawing in refrigerant gas, the discharge pressure of a discharge chamber for discharging refrigerant gas that is pressurized by the piston, and the control chamber pressure of a control chamber (crankcase) which houses the swash plate.
FIG. 6 shows an example of such a capacity control valve (referred to hereinafter as “Prior Art 1;” see Patent Document 1, for example) provided with discharge-side passages 73, 77 for communicating a discharge chamber and a control chamber; a first valve chamber 82 formed partway in the discharge-side passages; suction-side passages 71, 72 for communicating a suction chamber and the control chamber; a second valve chamber (working chamber) 83 formed partway in the suction-side passages; a valve body 81 formed so that a first valve part 76 disposed in the first valve chamber 82 to open and close the discharge-side passages 73, 77 and a second valve part 75 disposed in the second valve chamber 83 to open and close the suction-side passages 71, 71 integrally reciprocate while alternately opening and closing with respect to each other; a third valve chamber (capacity chamber) 84 formed partway in the suction-side passages 71, 72 closer to the control chamber; a pressure-sensitive body (bellows) 78 for exerting an urging force in the direction of extension (expansion) and contracting in conjunction with an increase in the surrounding pressure, the pressure-sensitive body being disposed in the third valve chamber; a valve seat (engaging part) 80 provided to a free end of the pressure-sensitive body in the extension and contraction direction thereof and having an annular seat surface; a third valve part (valve opening connection) 79 which moves integrally with the valve body 81 in the third valve chamber 84 and can open and close the suction-side passages by engagement and disengagement with the valve seat 80; a solenoid for exerting an electromagnetic driving force on the valve body 81; and other components.
This capacity control valve 70 is configured so that when the need arises to change the control chamber pressure during capacity control, the discharge chamber and the control chamber can be communicated and the pressure (control chamber pressure) Pc in the control chamber adjusted despite the variable-capacity compressor not being provided with a clutch mechanism. In this configuration, in a case in which the control chamber pressure Pc is elevated while the variable-capacity compressor is stopped, the third valve part (valve opening connection) 79 is disengaged from the valve seat (engaging part) 80 to open the suction-side passages and communicate the suction chamber and the control chamber.
In a case in which the swash plate variable-capacity compressor is started after having been stopped and left inactive for a long period of time, since liquid refrigerant (formed by condensation of refrigerant gas cooled during inactivity) accumulates in the control chamber (crankcase), refrigerant gas cannot be compressed and the set discharge amount maintained unless the liquid refrigerant is drained.
The liquid refrigerant in the control chamber (crankcase) must be drained as soon as possible in order to perform the desired capacity control immediately after starting.
In the capacity control valve 70 of Prior Art 1, when the solenoid S is turned off and the variable-capacity compressor is left stopped for a long time with the second valve part 75 blocking the communicating passages (suction-side passages) 71, 72, a state occurs in which liquid refrigerant is accumulated in the control chamber (crankcase) of the variable-capacity compressor. When the variable-capacity compressor is stopped for a long time, the pressure becomes uniform inside the variable-capacity compressor, and the control chamber pressure Pc becomes significantly higher than the suction pressure Ps and the control chamber pressure Pc that occurs during driving of the variable-capacity compressor.
In this state, when the solenoid S is turned on and the valve body 81 begins to move, the second valve part 75 moves in the opening direction at the same time that the first valve part 76 moves in the closing direction, and the liquid refrigerant in the control chamber of the variable-capacity compressor is drained. The control chamber pressure Pc causes the pressure-sensitive body 78 to contract, the third valve part 79 is disengaged from the valve seat 80, and the valve is opened. At that time, the second valve part 75 opens to open the communicating passages (suction-side passages) 72, 71, and the liquid refrigerant in the control chamber is therefore drained from the communicating passages (suction-side passages) 74, 72, 71 to the suction chamber of the variable-capacity compressor. When the control chamber pressure Pc reaches a predetermined level or below, the pressure-sensitive body 78 extends by elastic return, the valve seat 80 engages with the third valve part 79 to close the valve, and the communicating passages (suction-side passages) 74, 72, 71 are blocked.
FIG. 7 is a view showing the factors that determine the flow passage area of the third valve part 79 in FIG. 6, and shows a state in which the view of FIG. 6 is rotated 90° clockwise.
As shown in FIG. 7, the factors determining the flow passage area of the third valve part 79 in Prior Art 1 are the seal diameter D of the third valve part, the taper angle θ of the valve seat, the sphere radius r of the third valve part, and the stroke st of the third valve part.
Therefore, first examining the seal diameter D of the third valve part with reference to FIG. 8, the equilibrium of forces on the third valve part 79 is as expressed below in the case that the bellows effective area A and the seal area B of the third seal part are such that A>B.(A−B)Pc+BPs−Fb=0→Pc=(Fb−BPs)/(A−B)Since the third valve part 79 opens and control becomes impossible when the control chamber pressure Pc is equal to or higher than shown above, the bellows effective diameter and the seal diameter D of the third valve part 79 must be set so as to be the same in order to eliminate dependence on the control chamber pressure Pc. The seal diameter D ultimately cannot be changed, due to the limitation placed thereon by the bellows effective diameter.
Next examining the stroke st of the third valve part 79 with reference to FIG. 9, the equilibrium of forces when the third valve part 79 is stroked is such that when A=B, sincek·st=(A−B)Pc+BPs−Fb, thenst=(BPs−Fb)/k. The spring force Fb in this equation is expressed below.Fb=(A−C)Pc+Cps+(Fsol−Fspr1)
C: Seal area of the first valve part 76
Fsol: Solenoid thrust
Fspr1: Valve-opening spring force of a coil spring installed in the solenoid
Since the spring force Fb of the bellows is determined by the control chamber pressure Pc, the suction chamber pressure Ps, and the solenoid characteristics, it has been considered impossible to change the stroke st of the third valve part 79 without changing the control valve characteristics above.
For these reasons, conventional efforts to improve the flow passage area of the third valve part 79 have been concentrated entirely on optimizing the radius r of the third valve part 79 and the taper angle θ of the valve seat 80, and although these improvements make it possible to drain the liquid refrigerant faster than in a conventional capacity control valve (capacity control valve in which draining is accomplished solely through a fixed orifice for directly communicating the control chamber and the suction chamber) not structure so that the third valve part 79 can be opened, the ability to drain the liquid refrigerant is limited.
A technique has therefore been proposed by the present applicant in which an auxiliary communicating passage 85 is provided in a side surface of the third valve part 79, as shown in FIG. 10 (referred to hereinafter as “Prior Art 2;” see Patent Document 2, for example).
The technique of Prior Art 2 is capable of accelerating drainage of the liquid refrigerant, but during operation, the control chamber (crankcase) and the suction chamber are always communicated. A flow from the control chamber (crankcase) to the suction chamber therefore occurs, which adversely affects the swash plate control speed during control of the variable-capacity compressor.